The development of hydrocarbon producing wells requires the installation of well completion equipment to monitor and control the flow of fluids. The characteristics of the well are monitored by the completion equipment and are transmitted to the surface. The transmitted data is analyzed by a reservoir management system, and completion equipment such as valves, sliding sleeves, packers, and other completion tools are modified to control the well.
Electronic systems have been incorporated into well completion equipment. However, these downhole electronic systems do not adequately perform for the producing life of the well, which can typically last for ten or more years. When the electronic components in the equipment fails, reservoir management data is interrupted until the equipment is repaired. The repair of such equipment interrupts the operation of the well and increases production cost.
This limitation in the life span of downhole electronic systems is at least partially attributable to elevated temperatures found in certain wells. Downhole well temperatures can exceed 150 degrees Celcius, and these temperatures affect the operation of integrated circuits constructed with electronic components.
Efforts have been made to overcome the limitations of electronic devices at elevated temperatures by using fiber optics. One example is a down hole pressure gauge system which does not include downhole electronics. The gauge senses pressure through a response created by the change in refractive index of a material in response to pressure variations. This response is measured at the surface by monitoring the changes of an optical signal transmitted from the surface to the downhole gauge and back to the surface through a fiber optic cable. While optical systems may be beneficial with certain gauge types, optical systems are limited because many well bore characteristics cannot provide a direct optical response. Optical systems are also limited because sufficient power cannot be transmitted through such systems to manipulate downhole mechanical tools for controlling the flow of fluids. Consequently, optical systems cannot provide equivalent functionality to electronic solutions for the downhole processing of information or the regulation of power.
Although systems for extending the life span of electronic components in well completion tools have not been developed, well logging tools have used insulating flasks to shield electronic components from elevated well temperatures. For example, Dewar flasks maintain the electronic components within certain temperature ranges to prevent unstable circuit operation. Although Dewar flasks temporarily insulate the electronic components, the temperature inside the Dewar flask eventually equalizes with the well temperature.
Various concepts to improve the insulating performance of a Dewar flask have been proposed. For example, U.S. Pat. No. 3,265,893 to Rabson et al. (1966) described a well logging tool having a thermally conductive heat sink for stabilizing the temperature in the logging tool for up to twenty hours. U.S. Pat. No. 4,671,349 to Wolk (1987) described a heat transfer wick for cooling the components of a well logging instrument for up to six hours during the interval of greatest heat exposure.
Another concept for improving the performance of a Dewar flask was described in U.S. Pat. No. 3,488,970 to Hallenburg (1970). Electric components were insulated from the well temperature by a Dewar flask, and a pump transported water through a conduit to transfer internally generated heat from the electic components to a water reservoir positioned beneath the Dewar flask. Upper and lower temperature switches controlled the pump operation to heat and cool the Dewar flask within a selected temperature range. A thermoelectric cooling module transferred heat between the water reservoir and the borehole through the logging tool housing. The water reservoir was located at a position away from Dewar flask so that heat transferred by the thermoelectric cooling module was discharged at a position distant from the Dewar flask.
Another concept was described in DOE Technical Note DOE/TIC/EG-85/054 by Bennett entitled Improved Thermal Protection Apparatus for Electronics. This proposal used methanol carrying tubes to transfer heat from the electronics to a heat sink of ice so that the electronic components would be protected for up to ten hours at 235 degrees C. Bennett described another concept in a Journal of Energy Resources Technology article entitled Analytical Approach to Selecting and Designing a Minature Downhole Refrigerator (Dec. 1992).
None of these concepts describe a system for extending the life span of electronic components in well completion tools. Consequently, a need exists for an apparatus and method which extends the life span of electronic components exposed to elevated temperatures during the production life of a well.